Anatase

Recent advances in nano-technology and nano-additives can give enhanced properties to natural hydraulic lime (NHL), creating a multifunctional material. We have prepared a novel nanocomposite, made of a commercial mortar with 1 wt% and 5 wt% added titania nanoparticles (NPs). These TiO2 NPs are themselves doped with 1 mol% silver, to give the material enhanced photocatalytic and antimicrobial properties. The Ag-doped TiO2 NPs were made from a simple, costs effective, aqueous green nanosynthesis process, and the end material only contains 0.01–0.05% Ag. As this mortar is intended to both combat atmospheric pollution, and create more durable/lower maintenance building façades (plastering and finishing) by limiting attack from microorganisms and pollutants, its photocatalytic anti-pollution activity under solar and visible (no UV) light for nitrous oxide (NOx) and volatile organic compound (VOC) removal was studied. The addition of dopants did not significantly alter the physical properties or curing of the mortar, while it showed excellent photocatalytic activity under sunlight, The mortars with only 1 and 5 wt% additives degraded 10.6% and 21% NOx after 45 mins, respectively, comparing well to a value of 50% for a pure TiO2/Ag+ sample. They also degraded VOCs under visible light, of the kind used for lighting inside buildings, with no UV component. As the NPs are contained in the whole of the mortar layer, not just as a coating, if the surface is chipped or damaged this mortar will not loose its photocatalytic capabilities.

Copper dopants are varyingly reported to enhance photocatalytic activity at titanium dioxide surfaces through uncertain mechanisms. In order to interpret how copper doping might alter the performance of titanium dioxide photocatalysts in aqueous media we applied density functional theory methods to simulate surface units of doped anatase (101) planes. By including van der Waals interactions, we consider the energetics of adsorbed water at anatase surfaces in pristine and copper doped systems. Simulation results indicate that copper dopant at anatase (101) surfaces is most stable in a 2+ oxidation state and a disperse configuration, suggesting the formation of secondary CuO phases is energetically unfavourable. In agreement with previous reports, water at the studied surface is predicted to exhibit molecular adsorp-tion with this tendency slightly enhanced by copper. Results imply that the enhancement of photoactivity at anatase surfaces through Cu doping is more likely to arise from electronic interactions mediated by charge transfer and inter-bandgap states increasing photoexcitation and extending surface-hole lifetimes rather than through the increased density of adsorbed hydroxyl groups.

A novel, facile method based on a non-aqueous sol–gel solvothermal process has been developed to synthesise spherical TiO2 nanoparticles (NPs) in one pot. The reaction between titanium(IV) tert-butoxide (Ti[OC(CH3)3]4) and benzyl alcohol was a simple process, which resulted in the formation of highly crystalline titania NPs with a small size of only 6 nm, and with a correspondingly high surface area. The chemical formation mechanism of the metal oxide NPs has been proposed, and the degree of surface hydroxyls (–OH groups) has been examined. The products of the synthesis were characterised by X-ray powder diffraction (XRPD) using the advanced whole powder pattern modelling (WPPM) method, high-resolution transmission electron microscopy (HR-TEM), thermo-gravimetric analysis (TGA), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) spectroscopy. The photocatalytic activity (PCA) was evaluated in both the liquid–solid phase, by monitoring the degradation of an organic dye (methylene blue (MB)) under UV-light irradiation, and in the gas–solid phase, by following the degradation of 2-propanol under UV-and visible-light exposures. The synthesized titania powders not only exhibited excellent photocatalysis in the liquid–solid phase (under UV irradiation), but also possessed a superior PCA in the gas–solid phase under a visible-light exposure. The effects on the PCA of the very small crystalline domain size, surface composition and the presence of organic molecules due to the synthesis process of the TiO2 NPs were shown to account for this behaviour.

The black pigment of 112 Cucuteni A and Cucuteni B pottery has been analyzed through Raman spectroscopy. The black pigment contains pyrolusite and jacobsite; quartz and anatase have only accidentally been observed. Black Carbon was also identified, but only in two samples. The spherical or oblate black corpuscles discovered at Feteşti-La Schit (Suceava county) were analyzed by means of X-ray diffractometry and Raman spectroscopy. They consist of Mn ± Fe oxihydroxides and quartz. No Mn carbonates or silicates have been identified. The mineralogical composition of the pigment applied to the pottery shards, as well as that of the raw pigment, together with the use of the same pigment over a long period of time (1100 years), suggest the exploitation of a large sedimentary mineral deposit, such as the Mn sedimentary ores from Nikopol (Ukraine).

The light-induced phase transition of TiO2 nanoparticles from anatase to rutile structure is reported depending on the surrounding environment, the transition being accomplished under oxygen-poor conditions. The transition mechanism is interpreted in the framework of oxygen adsorption and desorption phenomena with the involvement of surface oxygen vacancies and F centers. It is shown that the observed phase transition is not thermally driven because the local temperature of the nanoparticles during irradiation is about 370 K (estimated through the Stokes to anti-Stokes Raman peaks ratio). On the contrary, the phase transition is initiated by intragap irradiation (with the exception of the red light one) that acts as TiO2 surface sensitizer, promoting the activation of the surface and the nucleation of rutile crystallites starting from two activated anatase neighboring nanoparticles.

In this paper, we report the comparison between nanosized TiO2 powders prepared via two different acidic conditions (i) pH2 (ii) pH4. The study presents the synthesis of nanosized TiO2 powder with anatase structure was derived from sol-gel process. Data concerning the effect of pH towards the development of TiO2 nanoparticles is reported. The samples were examined by SEM- EDAX, XRD, and FT-IR analysis. Surface morphological studies obtained from SEM micrograph. The Crystalline size of TiO2 powder has obtained for (i) pH 2 is ~3nm (ii) pH 4 is ~ 6nm at 400 ºC by controlling the acidity. In FT-IR, all the peaks observed were around 460-560 cm-1 due to stretching and bending vibrations of -OH groups. It was also found the pH of the solution affect the agglomeration of the particles

Článek přináší kompletní katalog dosud
známých zlomků tenkostěnné červené středověké
keramiky, která se svým výskytem v rámci Plzeňského
kraje zřejmě stále omezuje na okr. Klatovy.
Hlavním přínosem příspěvku je však zveřejnění
zajímavých výsledků petroarcheologické analýzy,
která odhalila přítomnost anatasu v červené
engobě.

Iron-doped TiO2 nanopowders with different doping amounts have been prepared by co-precipitation method followed by heat treatment. The obtained materials were structurally, morphologically and analytically characterized by X-ray diffraction (XRD), FT-Raman spectroscopy, diffuse reflectance spectroscopy (DRS) and energy dispersive X-ray spectroscopy (EDX) coupled to scanning electron microscopy (SEM). XRD analysis revealed the major presence of the anatasa crystalline phase for iron-doped and undoped TiO2. SEM confirmed particles sizes among the nanometer scale along with XRD data. The presence of iron ions was validated by EDX-SEM. Diffuse reflectance techniques were carried out to validate the shift of the band edge absorption spectrum of doped TiO2 nanoparticles towards the visible region and to confirm the presence of iron atoms in the TiO2 crystal lattice by the resulting variation of the band gap value of the doped materials. Photocatalytic activity of the nanoparticles under UV and visible radiation was evaluated by means of hydroxyl radicals production through indirect estimation using N,N-dimethyl-p-nitrosoaniline (PNDA)photo-discoloration experiments in aqueous dispersion. Samples containing 1.2 and 5.6 weight % Fe exhibited the highest activities in this study for both conditions.

Abstract Titanium dioxide photocatalysts co-modified with iron and nitrogen (Fe–N–TiO2) were produced via hydrothermal method using iron(III) nitrate nonahydrate and urea as iron and nitrogen sources, respectively. The effects of different dopant concentrations were investigated. The modified TiO2 catalysts were characterized for phase composition, surface morphology, specific surface area, degree of doping, charge states and bandgap energy combining various techniques. The results showed that controlled iron and nitrogen concentrations significantly altered the physicochemical properties of the catalysts. The photocatalysts displayed the anatase/rutile/brookite crystal phase mixture. The rutile and brookite phase contents increased with increasing iron content. On the other hand, increasing nitrogen content inhibited the formation of rutile and brookite phases and the catalysts displayed predominantly the anatase phase. High iron and low nitrogen contents led to the highest BET surface areas. The surface morphology changed from nanorice to spherical shape with increasing iron content. The bandgap energy of all Fe–N–TiO2 samples was in the range 2.7–3.1 eV, being lower than that of undoped TiO2 and pure anatase phase. Nitrogen was incorporated into the TiO2 lattice on interstitial positions (Ti–O–N). The iron, substituting some Ti4+ in the lattice was presented in Fe2+ and Fe3+ oxidation state, as confirmed by XANES measurements. The photocatalytic degradation of antibiotic ciprofloxacin was performed under visible light using a LED illumination source and nearly 70 % of the antibiotic was removed in 6 h by using the most active sample (2.5 %N–1.5 %Fe). As verified by photoluminescence results, the iron and nitrogen dopants synergistically enhanced the charge separation, since they promoted the formation of the different TiO2 phases.

The photocatalytic activity of anatase TiO 2 decorated with metal clusters has been widely documented, but the nature of the metal−metal oxide interface and reaction intermediates in catalytic processes are still not well understood. This in part is due to the fact that use of photoelectron spectroscopy to deduce the surface chemistry of catalytic systems has long been hampered by the huge pressure difference between real-world operation and the requirement of high vacuum for electron detection. Here, the in situ growth of silver nanoparticles on a model metal-oxide catalyst support and their reactivity with a CO/H 2 O gas mixture has been investigated in detail. Using synchrotron X-ray photoelectron spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, and scanning tunneling microscopy, the interaction of Ag with the anatase TiO 2 surface leads to metal-surface charge transfer and low mobility of Ag on the surface. Upon exposure to a 1.5 mbar CO/1.5 mbar H 2 O gas mixture, partial oxidation of the Ag clusters is observed. There is also evidence suggesting that a Ag−carbonyl species is formed during exposure of the Ag/TiO 2 surface to a CO/H 2 O gas mixture. ■ INTRODUCTION Metal clusters supported on well-ordered metal oxide surfaces are of great interest due to their application in a wide variety of fields, including photovoltaics, photocatalysis and transition metal catalysis. 1−6 Carbon monoxide (CO), in particular, is a major air pollutant which causes serious environmental and health concerns. As such, the catalytic oxidation of CO, to form CO 2 , is an important research area. 7−9 Noble metals supported on metal oxide ceramic supports have long been used for the catalytic conversion of CO to CO 2 , but the high cost of these metals remains a major issue. Noble metal clusters on oxide substrates are also of interest since they can produce high Schottky barriers which facilitate the capture of electrons. 10 As a result, such systems have been widely investigated, both experimentally and theoretically 5,11−19 as potential photo-catalytic materials which rely on rapid separation of photo-generated electrons and holes. The structural, chemical, and electronic properties at the interface between the metal clusters and the oxide support have all been shown to have a strong influence on catalytic and photocatalytic activity. 1,2,6,8,17−24 TiO 2 is an extremely versatile metal oxide: it is abundant, has low manufacturing costs, is chemically stable, and is both non-toxic and highly resistant to corrosion. The anatase polymorph of TiO 2 is widely used in catalysis due to its high photocatalytic activity, with the (101) facet being the most thermodynamically stable. 25 Often rutile and anatase TiO 2 powders are mixed, as in P25, 26 which increases the catalytic activity further due to the slight differences in the band gap energies of the two polymorphs. Ag is also non-toxic, catalytically active and has the highest thermal and electrical conductivity of all the noble metals. 27 In addition, Ag is not as costly as other noble metals. 9 Catalyst systems based on Ag/TiO 2 have been shown to efficiently catalyze reactions at solid−gas interfaces and in aqueous solutions. They have also been found to substantially enhance the photocatalytic capacity of TiO 2 for renewable energy generation and degradation of environmental pollutants. 20,28 Density functional theory (DFT+U) calculations of

The evidence that the Vinland Map is a modern forgery is not supported by the bi-pyramidal shape of the anatase crystals shown in the transmission electron micrograph of the ink of the Map. The proposed presence of a modern pigment was related to the identification of the anatase shown in the micrograph as having a rounded regular crystalline shape as contrasted to the bi-pyramidal shape that this paper has identified .

Článek přináší kompletní katalog dosud známých zlomků tenkostěnné červené středověké keramiky, která se svým výskytem v rámci Plzeňského kraje zřejmě stále omezuje na okr. Klatovy. Hlavním přínosem příspěvku je však zveřejnění zajímavých výsledků petroarcheologické analýzy, která odhalila přítomnost anatasu v červené engobě.

In this research we report the gas-sensing properties of TiO2-x/TiO2-based hetero-structure, which was ‘self-heated’ by current that at constant potential passed through the structure. Amperometric measurements were applied for the evaluation of sensor response towards ethanol, methanol, n-propanol and acetone gases/vapours. The sensitivity towards these gases was based on electrical resistance changes, which were determined by amperometric measurements of current at fixed voltage applied between Pt-based contacts/electrodes deposited on the TiO2-x/TiO2-based layer. X-ray diffraction (XRD) analysis revealed the formation of TiO2-x/TiO2-based hetero-structure, which is mainly based on Ti3O5/TiO2 formed during the hydro-thermal oxidation-based sensing-layer preparation process. Additionally, photoluminescence and time-resolved photoluminescence decay kinetics-based signals of this sensing structure revealed the presence of TiO2 mainly in the anatase phase in the TiO2-x/TiO2-based hete...

Titania hydrolysates prepared from the hydrolysis of both unmodified and modified tetraisopropoxytitanium(iv) are shown by both FT-Raman spectroscopy and X-ray diffraction to be amorphous with no long range ordering. The Raman hydrolysate spectra show three broad bands, consisting of multiple components, at Raman shifts of ∼210, 440 and 570 cm−1. These bands do not correspond with any known phase of titania. Thermal analysis shows broad endothermic peaks centred at 106–136°C and extending to ≥200°C for each of the hydrolysates and is attributed to dehydration and loss of water. Strong, broad exothermic peaks are observed in the modified hydrolysate curves, in the 310–340°C temperature range and are attributed to the combustion of the residual surface adsorbed organics. Weight loss occurred during these exotherms. Crystallisation of the disordered hydrolysates into anatase occurs in the 500–600°C temperature range. The anatase → rutile phase transition was found between 665°C and 691°C.

Amongst nanomaterials, metal oxides play an increasingly dominant role, with titanium dioxide (titania, TiO2) being widely used for various applications, such as light-to-energy conversion and storage, and photocatalysis. In this work, TiO2 has been synthesised via an aqueous sol–gel method, using three different mineral acids (HNO 3 , HCl and HBr) to peptise the sol, and hence provide counter-ions. Dried sols were thermally treated at three different temperatures (450, 600 and 800 °C), using three different dwell times (2, 4, and 8 h). Advanced X-ray methods were used to monitor the effect that the counter-ions had on the anatase-to-rutile phase transformation (ART). Quantitative phase analysis (QPA) using the Rietveld method was applied to assess the true amount of crystalline phases in the systems, and the amount of amorphous phase. Furthermore, the average crystalline domain diameter was also investigated, using whole powder pattern modelling (WPPM). With the advanced XRPD data (actual crystalline phase weight fraction in the samples and their average domain diameter and size distribution), it was possible to carry out a semi-quantitative study of the ART transformation kinetics. At a low temperature of 75 °C, the Cl − counter-ion was the most favourable to obtain anatase as the major crystalline phase, delaying the onset of the ART. Conversely, the Br − ions, maintained more anatase at 450 °C, with a lower ART rate. In general, halides were more effective in delaying the ART than NO3 − counterions. Moreover, we observed an inverse linear relationship between the lattice volume expansion of rutile and the increase of its crystalline domain size at 450 and 600 °C isotherms. As the domain sizes increased with temperature, this effect reversed and became a direct linear dependence at the 800 °C isotherm, suggesting a critical size limit <90 nm for this effect.

We report on the preparation of a new photocatalyst by impregnation of size-selected TiO2 nanoparticles into monolithic ultraporous alumina of θ and α polymorphs. The alumina matrix is prepared by selective surface oxidation of liquid Hg-alloys in a humid atmosphere at room temperature with subsequent annealing at 1100–1300°C. An additional treatment with trimethylethoxysilane was used to mechanically reinforce the ultraporous

ABSTRACT The optical absorption and photoluminescence of anatase and rutile TiO2 were studied at room temperature. TiO2 nanocrystalline powders were synthesized in the form of pure anatase or rutile. The samples were characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL) methods. The PL spectra were studied under the intensive UV (3.68eV) laser excitation. Some interesting features in the PL spectra including the well-resolved peaks of excitonic and band–band transitions in TiO2 anatase and rutile were observed, to our knowledge, for the first time. It is shown that PL bands including peaks at 2.71–2.81 eV and its phonon replicas in anatase and rutile TiO2 arise from the excitonic e--h+ recombination via oxygen vacancies. The excitonic peak at 2.91 eV is attributed to the recombination of self-trapped excitons in anatase or free excitons in rutile TiO2. The PL peaks within 3.0–3.3 eV in anatase TiO2 are ascribed to indirect allowed transitions due to the band-band e--h+ recombination. The peaks at 3.03 eV and 3.26 eV are attributed to the free exciton emission near the fundamental band edge of rutile and anatase TiO2, respectively. The influence of TiO2 crystal structure and calcinations temperature on the PL spectra is discussed.

Shock-wave-einduced phase transformations in nanostructural titanium dioxide TiO2 (anatase)
powders of two types have been studied by Raman spectroscopy. It is established that, at a shock-wave commpression to 42 GPa, anatase particles can either transform into a columbite phase or exhibit amorphization.

Abstract The photocatalyzed oxidation of indole (1) in an aqueous suspension of titanium dioxide has been investigated and an attempt has been made to identify the products formed during the photooxidation process by gas chromatographic–mass spectrometric (GC–MS) ...

Abstract Introducing oxygen vacancies (Vo) into TiO2 photocatalyst has been considered an effective strategy for improving co-catalyst-free solar photocatalytic activity. However, the methods used to synthesize it require high pressure/temperature and/or hazardous/costly reagents. Here we propose Vo introduction, concomitant with N-doping in TiO2, as an alternative strategy for achieving efficient co-catalyst-free solar photocatalytic activity under less extreme conditions. After calcination at 450 °C of mesoporous spherical assemblies of a layered titanate nanosheet containing N,N-dimethylformamide as its synthesis solvent in the structure, we successfully synthesized mesoporous spherical assemblies of nanosheets composed of anatase TiO2 nanoparticles with Vo mediated by N doping. This material exhibits good co-catalyst-free solar photocatalytic activity for hydrogen evolution via water splitting under irradiation with simulated solar light, which is considerably higher than that of typical co-catalyst-free defective TiO2 materials. We discuss the possible role of the introduced Vo in facilitating charge separation and raising photocatalytic efficiency.

A pure TiO2 thin film (100–120 nm) was made from a green aqueous sol–gel precursor on FTO glass and calcined at 430 °C. It was a mix of amorphous, anatase, rutile and brookite TiO2 phases, and exhibited very good electrochromic properties over visible and NIR wavelengths with an applied bias of +0.1 V to −1.5 V. It was highly transparent showing excellent coloration with applied voltage, with transmittance modulation (ΔT) = 69.7% at 550 nm, 86% at 700 nm and an overall ΔT between 400–1650 nm of 60%, giving a very large change in optical density (ΔOD) of 1.4 at 550 nm and 2.4 at 700 nm. Cyclic voltammograms had typical peaks for TiO2 at −1.3 V for colouration and −0.9 V for bleaching, with a high separation of 0.37 V between peaks, and a charge density after charging for 25 min of Qc = 50 mC cm−2. After only 60 s and 120 s at −1.5 V, inserted charge values of 17.6 and 22 mC cm−2 were observed, leading to a high colouration efficiency (CE) of 55.9 cm2 C−1 at 550 nm. These ΔOD, ΔT, Qc and CE values are superior to any previously reported for crystalline sol–gel TiO2 films. They also possessed rapid switching times for bleaching and colouring of τb90% = 10 s and τc90% = 55 s, comparable to the best previously reported sol–gel anatase-based TiO2 films. This makes this nanomaterial an excellent candidate for smart windows and other electrochromic devices and applications.